In the prior art, in order to address the cost and coverage issues of network deployment, various manufacturers and standardization organizations have introduced a Relay Node (RN) to a cellular system to extend the coverage. The RN in the prior art is referred to as a fixed relay node which does not support mobility. FIG. 1 is a network architecture of a Long Term Evolution-Advanced (LTE-A) system with an RN deployment, where the RN is connected to a core network via a donor cell served by a Donor evolved Node B (DeNB). There is no direct wired interface between the RN and the core network. Each RN can control one or more cells. In this architecture, an interface between a User Equipment (UE) and the RN is referred to as a Uu interface, and an interface between the RN and the DeNB is referred to as a Un interface. The DeNB is integrated with part of functions of a Packet Data Network Gateway (PGW) and a Serving Gateway (SGW).
The RN has a dual-identity as a UE and an evolved Node B (eNB). As described in the protocol 3GPP TS 36.300, the RN is started in a process which can be described in two phases: in a first phase, the RN access to any evolved Node B as a UE, registered with the network, accesses an RN Operation and Maintenance (OAM) system and downloads a list of accessible Donor evolved Node B (DeNB) cells, and then the RN is deregistered with the network; and in a second phase, the RN selects one of the accessible DeNB cells and establishes a Radio Resource Control (RRC) connection with the DeNB. The DeNB selects an appropriate Mobility Management Entity (MME) for the UE, and the MME selects the DeNB as an SGW and a PGW of the RN. The DeNB establishes a default bearer and necessary dedicated bearer for the RN, and then the OAM downloads node configuration information to the RN and configures the RN. The RN can operate normally as an evolved Node B after establishing necessary S1 and X2 interfaces.
In the first phase, the eNB and the MME serving the RN can be legacy nodes, that is, they may not support the RN. In the second phase, the evolved Node B and the MME, which are accessed by the RN, must support the RN. Moreover in this phase, the DeNB sends IP addresses of the embedded PGW and the SGW to the MME, and the MME selects the DeNB as the PGW and the SGW of the RN according to the received IP addresses and establishes the necessary interfaces thereto.
In the process of starting the RN, subscription data of the RN sent from a Home Subscriber Server (HSS) to the MME includes information indicating that the subscription data is for the RN and a special Access Point Name (APN) referring to the PGW for connection with the OAM. In the first phase, the MME uses the special APN to select the PGW accessible to the OAM so that the RN accesses the OAM and downloads the initial configuration information. In the second phase, the MME receives RN indication information sent from the DeNB and thus ignores the APN information in the subscription data and selects the PGW and the SGW using the IP addresses of the PGW and the SGW reported from the DeNB.
In order to address the problems of a poor signal coverage, frequent handovers, etc., in a high-speed mobile environment, a relay node supporting mobility, i.e., a mobile RN, can be deployed on a vehicle body moving at a high speed to enhance a signal quality inside the vehicle body, and the number of handover and location update can be decreased by a group handover.
FIG. 2 is a schematic diagram of a node relationship for an RN applicable to a high-speed mobile environment. Firstly the RN accesses to the network like a UE, and the network establishes an Evolved Packet System (EPS) bearer for the RN. The RN accesses an OAM and downloads necessary configuration data. Then the RN establishes necessary interfaces with a core network and configures Uu interface parameters to thereby become an evolved Node B. From the perspective of a UE, the RN is a serving evolved Node B of the UE. When the UE accesses the RN, all the data of the UE is mapped onto a bearer of the RN and transferred to a next-hop node through a PGW of the RN.
It shall be noted that the DeNB deployed in the high-speed mobile scenario may not be provided with the functions of the PGW and the SGW of the RN.
The inventors have identified during making of the invention the following technical problems in the prior art:
in the second phase of starting the RN, the MME selects the DeNB as the PGW and the SGW of the RN according to the IP addresses of the PGW and the SGW reported from the DeNB. However the DeNB deployed in the high-speed mobile scenario may not be integrated with the functions of the SGW/PGW of the mobile RN, and it is very likely that the PGW of the mobile RN is located in the core network, so the DeNB is typically not aware of the IP address of the SGW/PGW, and consequently it is not feasible to select the PGW and the SGW for the mobile RN still in the mechanism to report the IP address of the gateway from the DeNB in the prior art.